Tai otoshi means literally "body drop"... (the body drop that's described by the name is the tori's dropping body, by the way, not the aite only) a true taiotoshi doesn't need to block the leg/ankle of the aite. It can be done that way but shouldn't really be necessary and when necessary it should be a last minute placement as the aite's leg is thrusting into a recovery cycle. Any sumi otoshi can be done as a dropping body or it can be in the floating phase. Sumi is to a corner and these waza are pretty much the same. Some have called these types of waza as Kokyunage... I think all waza done really well could be called "kokyunage", by the way.

Mifune, Kyuzo sensei was known to throw taiotoshi without any blocking of the uke's foot/ankle/leg. The naming of waza and in judo, for example, it's inclusion in a particular type of waza category is very telling... for example, taiotoshi is not thought of as ashiwaza. Another example, many lower level judoka throw uchimata with actions that are really koshiwaza, or hip throws. Uchimata is an ashiwaza.